1. Field of the Invention
The present invention relates to a method of forming a wiring pattern and a method of manufacturing a thin film transistor (TFT) substrate using the same. More particularly, the present invention relates to a method of forming a wiring pattern by use of a screen printing method, and a method of manufacturing a TFT substrate using the same.
2. Description of the Related Art
In a color liquid crystal display panel of a color liquid crystal display, manufacturing of a high-definition panel has been underway. For manufacturing of the high-definition panel, conventionally, there has been adopted a method of narrowing a pitch between pixels of a color filter and a thin film transistor (TFT) and reducing a line width of a black matrix (BM) of the color filter and line widths of a data line and a gate line of the TFT.
Moreover, in manufacturing of the color liquid crystal display panel, manufacturing of a TFT substrate occupies about 60 to 70% of manufacturing lead-time.
Thus, from the aspect of reducing the manufacturing lead-time of the color liquid crystal display panel, there has been strongly demanded reduction of the manufacturing lead-time including review of a method of manufacturing the TFT substrate.
Generally, the TFT substrate is manufactured in such a manner that, after required kinds of films such as a metal film and a semiconductor film are deposited on a glass substrate, etching and patterning of the metal film and the semiconductor film are repeated by use of a method called photolithography. In the method of manufacturing the TFT substrate, utility factor for a photoresist used as a protective film in etching of the metal film and the semiconductor film is very small. Specifically, the photoresist is applied onto the entire surfaces of the metal film and the semiconductor film which are deposited on the glass substrate, and is patterned to have shapes of a wiring and an electrode by exposure and development. In this event, the photoresist left as the protective film is less than 1% of the photoresist applied. In other words, less than 1% of the photoresist is used and the rest is discarded. As a result, the photoresist formation process is a cause of an increase of the manufacturing cost. Moreover, the TFT substrate is manufactured by repeating the steps of forming kinds of films required for a pattern and of applying, exposing, developing and etching a resist. Thus, manufacturing lead-time is increased.
In order to solve the foregoing problems, there has been disclosed a method of forming required kinds of films on the entire surface of a glass substrate and then printing a resist directly in a pattern of an electrode and a wiring on the films.
For example, Japanese Patent Laid-Open No. 2002-341376 (hereinafter referred to as Patent Document 1) discloses a technology of printing a resin (toner) containing metal particles onto a substrate by use of electrophotography using a photoconductor drum, and then forming a gate electrode of a substrate for a semiconductor element (a TFT substrate) by breaking down the resin at a high temperature.
Moreover, Japanese Patent Laid-Open No. 2002-268585 (hereinafter referred to as Patent Document 2) discloses a technology of forming a gate electrode of an active matrix substrate used in a liquid crystal display or the like by forming a resist pattern by use of an intaglio offset printing method and etching a metal film.
However, the technologies described above can only be applied to a relatively large pattern. For example, it has been difficult to apply the technologies to a TFT substrate which enables high-definition display such as that demanded in market. Moreover, there has been considered a method of forming a wiring pattern of a TFT substrate by use of an etching resist formed by a screen printing method.
A method of manufacturing a TFT substrate will be described, which uses a conventional screen printing method to form an etching resist for wiring formation.
FIGS. 1A and 1B are cross-sectional views of a main part of a substrate, showing the method of manufacturing a TFT substrate, which uses the conventional screen printing method to form the etching resist for wiring formation. As shown in FIG. 1A, a first wiring pattern 702 is formed on a glass substrate 701. Next, by use of a sputtering method, a CVD method or the like, a wiring metal film 704 for a second wiring pattern such as an electrode and a semiconductor layer is formed on the first wiring pattern 702 with an interlayer insulating film 703 interposed therebetween. Thereafter, a resist pattern 705 is formed by use of the screen printing method. Subsequently, the entire structure including the glass substrate 701 is baked in a furnace or the like to harden the resist pattern 705.
Next, an unnecessary portion of the wiring metal film 704 on the glass substrate 701 is removed by etching. Thereafter, the resist pattern 705 is removed by use of a stripping agent.
Accordingly, a multilayer wiring of the TFT substrate is formed by sequentially repeating the steps of forming an interlayer insulating film and a wiring metal film, forming a resist pattern and etching.
In the conventional method of manufacturing a TFT substrate as described above, if a pattern is printed in a step part 708 formed by intersection of wirings, as shown in FIG. 1A, spaces 706 may be generated under the resist pattern 705. The spaces 706 are generated because a resist used for printing normally has a viscosity higher than that of a resist for a spin coater used in an application step of a usual photoresist method and the like, and has a poor coating coverage for irregularities, step portions and the like.
Accordingly, as shown in FIG. 1B, in the step portion, a defective part 707 is likely to be caused by cutting-off of the resist pattern 705. As a result, a portion of the wiring metal film, which should normally be left behind, is also etched by the subsequent etching step. Thus, a wiring defect or disconnection occurs.